This invention relates to a scroll-type hydraulic machine.
Before describing the present invention, the operating principles of a scroll-type hydraulic machine will be briefly explained.
FIGS. 1A to 1D show fundamental components of a scroll-type compressor, which is one application of a hydraulic machine, at successive operating angular positions. As shown in these figures, the compressor is composed of a stationary scroll 1 having a fixed center O and an orbiting scroll 2 having an orbiting point O'. Compression chambers 4 are formed between the stationary scroll 1 and the orbiting scroll 2, and a discharge port 3 is provided at a center portion of the stationary scroll 1. The wraps of the scrolls 1 and 2 may have the form of an involute or a combination of involutes and acrs. The two wraps have complementary (mirror image) configurations.
In operation, the stationary scroll 1 and the orbiting scroll 2 are interleaved as shown and the orbiting scroll 2 is made to orbit continuously with respect to the stationary scroll 1 from a starting position (0.degree.) depicted in FIG. 1A through angular positions of 90.degree. (FIG. 1B), 180.degree. (FIG. 1C) and 270.degree. (FIG. 1D), without charging its attitude with respect to the stationary scroll 1. With such orbital movement of the orbiting scroll 2, volumes of the compression chambers 4 are periodically reduced, and hence the intake fluid is compressed. The compressed fluid is discharged from the discharge port 3.
During this operation, the discharge between the center O and the point O' is constant and can be represented by: ##EQU1## where p corresponds to the pitch of the wraps and t is the wall thickness of each wrap.
In order to minimize the thrust forces acting in a scroll-type hydraulic machine or compressor having a large capacity, a structure has been proposed in which the orbiting scrolls are arranged in a back-to-back relationship to cancel out the thrust forces acting thereon. Examples of such structure are disclosed in U.S. Pat. Nos. 801,182, 3,011,694 and 4,192,152. In order to facilitate an understanding of the background of the present invention, the structure having the back-to-back arranged orbiting scrolls will be described briefly with reference to FIG. 2, which shows schematically an example of such a structure as disclosed in U.S. Pat. No. 4,192,152.
In FIG. 2, a pair of stationary scrolls 1 having scroll wraps 5 which are complementary in shape are fixedly secured to each other by bolts 14 with the scroll wraps facing one another with a space therebetween. An orbiting scroll 2 is formed on opposite surfaces thereof with orbiting scroll wraps 6, which are of complementary shapes. The orbiting scroll 2 is disposed in the space between the stationary scrolls. A plurality of compression chambers 4 are formed between the stationary scroll wraps 5 and the scroll wraps 6. Discharge ports 3 for the compressed fluid (such as air) are formed at center portion of the stationary scrolls 1. Discharge tubes 15 are connected to respective ones of the ports 3. An intake port 16 is formed at suitable position at the periphery of one of the stationary scrolls 1, to which an intake pipe 17 is connected. An intake chamber 18 is formed around the intake port 16 in the space formed between the stationary scrolls 1. A crankshaft 7 having an eccentric portion is supported by bearings 9, 10 and 11 provided in the stationary scrolls 1 and driven through a coupling 12 by a driving source 13. The eccentric portion of the crankshaft 7 is supported by a bearing 8 provided in the orbiting scroll 2. A balance weight 19 is attached to the eccentric portion of the crankshaft 7 to balance the centrifugal forces acting on the orbiting scroll 2 during the operation of the machine.
In operation, the crankshaft 7 is rotated by the driving source 13, which may be an electric motor, internal combustion engine, turbine or the like. When the crankshaft 7 rotates, the orbiting scroll 2 is made to orbit through the bearing 8 due to the eccentric rotation of the eccentric portion thereof. Hence, compression occurs on both sides of the orbiting scroll. The pressure in the compression chambers 4 increases with their movements towards the center portion of the machine. The compressed fluid is discharged from the discharge ports 3 through the discharge tubes 15. At the same time, fluid intake occurs through the tube 17 and the intake port 16 to the intake chamber 18, which is then fed to the compression chambers 4. The centrifugal force acting on the orbiting scroll 2 which is generated during the operation thereof is statically as well as dynamically balanced by the balance weight 19 shown in FIG. 2.
Since the compression chambers 4 are formed symmetrically, that is, with a mirror-image relationship on opposite sides of the orbiting scroll 2, the pressure distributions in the compression chambers 4 on the two sides are similar, and thus there are no thrust forces acting on the orbiting scroll 2 as a whole. This construction is particularly effective when the operating speed of the orbiting scroll is low and the thrust load is large because, in such a case, it is very difficult to employ a thrust bearing.
Although the conventional structure as described above is advantageous due to the fact that no thrust forces are produced, there are still problems in actual practice. Particularly, it is impossible as a practical matter to manufacture the orbiting scroll 2 having the mirror-image scroll wraps 6 on the opposite sides thereof with a high precision, and it is very difficult to assemble the orbiting scroll with the stationary scroll 1 having the wraps 5 with precisely adjusted radial gaps between the orbiting scroll wraps 6 and the stationary scroll wraps 5 on the two sides of the orbiting scroll. Therefore, the conventional scroll-type machine manufactured without taking such matters as mentioned above into consideration has not been entirely satisfactory. Particularly, when the crank bearings 9, 10 and 11 supporting the crankshaft 7 are provided in the stationary scrolls 1, the position of one of the stationary scrolls relative to the other is determined by the positions of the bearings in the stationary scrolls 1 and the position of the orbiting scrolls 2 relative to the stationary scrolls is determined by its coupling to the crankshaft 7. Thus, very precise adjustment of the radial gaps between the orbiting scroll and the stationary scroll is impossible as a practical matter.
Another important problem resides in the driving system for the orbiting scroll. In FIG. 2, a single crank mechanism is shown. In a case where a plurality of crank mechanisms are provided, arranged equiangularly, the eccentric center of the respective crankshafts 7 of the plural mechanisms must be precisely determined, otherwise normal operation of the machine itself cannot be attained.